The cats aren't having any of it, so it's lucky for both Cassandra and, by sheer accident, the Doctor, that she has a Plan B.

Her lackey Chip pulls a lever and every cell door on the row springs open, including the Doctor's, who of course immediately proceeds to yell at her about what she's done, which is to give the whole system a shot of adrenaline, waking up an army of plague-carriers who'd like nothing better than to infect every last one of them.

No way in hell is Cassandra sticking around to watch this. She flees, leaving the Doctor shouting something about not touching them in her wake.